Automatic telephone system



R. G. RICHARDSON ET AL AUTOMATIC TELEPHONE SYSTEM Origifial iled Feb. 23. 1922 10 Sheets-Sheet l H1: in: EHichardscm W511 Nov. 13, 1928. 1,691,410

R. G. RICHARDSON ET AL AUTOMATIC TELEPHONE SYSTEM or'giggl F'igLed Feb. 25. 722 10 Sheets-She t 2 H3 3 LLQ Ruin: ERichardsun Maia/9M H117.

R. G. RICHARDSON ET AL.

AUTOMATIC TELEPHONE SYSTEM I NOV. 13, 1928.

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Nov. 13, 1928.

R. G. RICHARDSON ET AL AUTOMATIC TELEPHONE SYSTEM Original Filed Feb. 23. 1922 10 Sheets-Sheet 5 Inusn ur's max" 111 LNeZsun Raine 5': Hishar'dsun U5 U (377 A38 1,69L4i0 R. G. RHCHARDSON ET AL AUTOMATIC TELEPHONE SYSTEM Original Filed Feb. 25, 1922 10 Sheets-Sheet 6 ---Inuinzurs I I'aFHE LNeZsun Raina EEid-Lar'dsun 4 .4

Nov. 13, 1928.

R. G. RICHARDSON ET AL AUTOMATIC TELEPHONE SYSTEM Original Filed Feb. 23. 1922 www NN Imrsniurs M'aFIin'LNeZsun Raine ERicZ-Lardsun Y1,69l,41@ G. RICHARDSON ET AL 7 AUTOMATIC TELEPHONE SYSTEM Original Filed Feb. 23. 1922 10 SheetsSheet 8 Nov. 13, 1928. 1,691,410

R. G. RICHARDSON ET AL AUTOMATI C TELEPHONE SYS TEM Original Filed Feb. 23. 1922 10 Sheets-Sheet 9 Raine 5. Rial-Larissa Nov" '13, 192s.- 1,691,410

R. G. RICHARDSON ET AL AUTOMATIC TELEPHONE SYSTEM Original Filed 'Feb. 23. 1922 10 Sheets-Sheet 10 FIG. 2 F/GZ FIG. 4 FIG 5 FIG.

FIG. 6 F/G 8 FIG 7 FIG 9 Patented Nov. 13, 1928.

UNITED STA Original application filed. re

TES

PATENT OFFICE.

or CHICAGO,

AND MARTIN L. NELSON, 0F PARK RIDGE, BY MESNE ASSIGNMENTS,

A CORPORATION OF DELAWARE.

TO AUTOI IIATIC ELECTRIC, INC.,

AUTOMATIC TELEPHONE SYSTEM.

The present invention relates in general to automatic telephone I systems of the well-known particularly to Strowger or decimal systems, but more type; and the general object of the invention is the provision of new and improved ci rcuit arrangements and apparatus which enable the Strowger system to be conveniently used in large systems having complex multi-olfie networks.

The Strowger system has been used for,

large multi-oilice systems with considerable success,

before this, and but its use under such conditions is not all that could be' desired, owing to the inflexibility of the inter-office trunking, which must correspond to the directory numb ciation of the trunking ering. The rigid assowith the numbering is also objectionable where existing manual networks are converted to automatic operation, for in such cases it is usually deslrable to retain the old manual exchange names as part of the automatic the occurrence of similar names areas and dissimilar trunking In order to avoid numbering system, and in difierent names in the same area renders it exceedingly difiicult to arrange the on aneconomical and efiicient basis.

difiiculties of the foregoing nature, it is proposed herein to provide registering and translating equipment in each ofiice which is adapted to register thedigits in called numbers as and which is adapted which have to they are dialled,- to translate those digits do with the office selection or inter-oilice trunking into suitable office codes. The registering and translating devlc es thus tween Offices on to arrange the most eflicient basis, and

the trunking beentirely without reference to the directory numbering.

The invention is illustrated in the accompanying drawings, comprisi Inclusive, of which the diagrams of'the a schematic diagram 5 ng Figs. 1 to 12, first ten are circuit Fig. 11 is aparatus,

' the various rowing how sheets should be joined together, while Fig.

12 is a front view of device, showing the Referring to Fig. automatic substation numbering 1, the substation A 18 an the subscribers calling of the dial.

of the usual type, having the usual transmitter, receiver, an

ringer, and a calli ng device or impulse shown in bruary 23,-. 1922, Serial No. 538,551. Divided and this application filed August e, 1928. Serial No. 297,609.

sender CD for controlling the automatic switches.

. The reference character C indicates a rotary Qline switch, which is individual to the line of station A,'and whichresponds automatically when the receiver is removed thereat to initiate a call to extend the line to an idle first selector. The line switch C is of the well-known rotary type, in which the wipers have no normal position and move in a forward direction only.

In common with other similar line switches the line switch C has access to a plurality of trunk lines, one of which is the drawings as extending by way of the relay e k uipment D to the first selector E, Fig. 2. he relay equipment Dis inserted in the trunk in order to provide for connecting and disconnecting a registering and translating equipment at the proper time. The first selector E is a Strowger vertical and rotary switch of the usual type, having its bank contacts arranged in ten horizontal rows or levels. Second selectors E and E also shown in Fig. 2, are similar tothefirst selector E At the right of. the selector E is shown a trunk line extending to an operators position and there terminating in jack J The lower line switch C and a repeater R. The former is accessible to the second selector E and other similar selectors, and in construction is similar to the primary'line switch C. The repeater R is adapted to repeat automatic switch operating impulses received over the two sides of the trunk in series, and is provided with a repeating coil in lieu of the condensers which have been widely used heretofore. The upper half of Fig. 3 shows third and fourth selectors ".E- and E, which are similar to the selectors already described, and the repeater R which is the same as the repeater R.

Fig. 4 shows the third fourth selectors E and 15*, together with the repeater R all of which are the same as the selectors and repeaters previouslydescribed.

Fig. 5 shows an automatic connector switch H, which is of the usual Strowger vertical selector E, and the the advanced out of their ing and extending to the first sets of contacts in its bank,

, cuits for the magnets.

and rotary type, and which is adapted to respond to two successive series of impulses inorder to direct its wipers to the contacts ofa particular line to whichit has access, .difi'ering in this respect from the selector switches hereinbefore referred to, which respond to only one series of impulses and which have an automatic trunk hunting movement. The mechanical construction of the connector H is, however, very similar to that of the selectors. The rotary line switch C is individual to the line of station A and is similar to the line switch C, Fig. 1.

A complete set of registering and translating equipment may be called a director from its function of directing or routing calls to their proper destinations. One such complete equipment, or director, is shown in Figs. 6, 7 8 and 9, and the lower half of Fig. 1. This director comprises the finder F, F ig. 1; the master digit controller M Fig. 6; the A impulse register M Fig. 6; nine Strowger switch mechanisms for registering B and C impulses, of which one is shown at H Fig. 7; the thousands register M a hundred register M, a tens register M,

and a units register M all of which are shown in Fig. 6; an impulsesending switch S Fig. 8; a sequence switch S, Fig. 9; and ghe i zitermediate distributin frame I.D.F,

In the mechanical construction the finder switch F is similar to the rotary line switch C. This finder switch, together with the finders which are allotted to other directors, has access to a'group of trunk lines, one of which is the trunk line shown in the drawselector E has twenty-five which is the usual size, there would be twenty-five trunks in the group to which the finder has access, requiring the provision of about six-or seven directors to handle the traffic. It will be understood that'any other convenient method ssuming that the finder F .of associating the directors with the trunks may be ein loyed if desired, such for example as t'ie scheme of pro\-'iding rotary switches individual to the trunks which hunt for idle directors.

The master digit controller M the A imulse register M and the four-digit registers ll I" to M, inclusive, are simple ten-point step by step switches, each of which is provided with an operatin r magnet and a release magnet, and a set of off normal springs which are. operated when the switch wipers are normal position.

The Strowgerswitch mechanism IP is the same in mechanical construction as an ordinary Strowger connector switch; that is, it has both vertical and rotary directive movements. Only sufficient relays are provided, however, to control the operating cir- The connector H is shown in Figs. ('5 and 8.-

provided with four wipers, indicated by reference characters 220 to 223, inclusive, and shown nearthe center of the drawing, F1 7, which also shows a portion of the first and second levels of the bank to which these wipers have access. Eachof the other eight Strowger switch mechanisms in this particular director is also provided with four wipers, and the wipers of all the switches are connected in multiple. The banks, however, are not multipled, but each set of four contacts has a set of four individual wires which is terminated on the left hand side of the I.D.F. The drawing shows four conductors coming from the first set of contacts in the second level of the switch H and tcrminating inthe first four contacts on the I.D.F, four wires coming from the second set of contacts in the second level and tenni nating in the next four contacts on the I.D.F and four wires coming from the first set of contacts in the first level and tenninating in the next four contacts on the I.D.F. The bank of each Strowger switch in the director is wired up to the left hand side of the I.D.F, the same as has been explained in the case of the switch H thus it will be seen that therewill be four hundred wires coming from each switch, or thirtysix hundred wires in all. There are also some additional wires coming from the relays shown in Fig. 9, which will be explained hereinafter.

The right hand side of the I.D.F. consists of thirteen continuous strips or bus-bars or multipled terminals, with facilities for cross-connecting any terminal on the left hand side with any one of the thirteen busbars. The first ten bus-bars correspond to the ten digits, 1 to 0, inclusive, and are so marked in the drawing. These bus-bars are connected in multiple with the banks of the register switches M to M inclusive, and with the bank of the sending switch S, as is The three lower bus-bars are provided for special purposes which will be explained fully later on.

The sending switch S, Fig. 8, and the sequence switch S Fig. 9, are rotary switches similar in mechanical construction to the line switch C, Fig. 1; thatis, the wipers move in a fordward direction only. Each of these switches, however, has a normal or home position in which it stands when at rest.

The repeater B, Fig. 10, is not included in the main layout of the system, but is provided for a special purpose as will be pointed out hereinafter. i I i The invention is illustrated as applied to what is'known as a 10,000,000 line system; that is, one in which each telephone number consists of seven digits. or other characters. This numbering scheme providcsfor a markimum of one thousand 10,000 line offices, which is large enough for the very largest exchange areas. In order to assist the subscribers in remembering the telephone numbers, the first three letters of the exchange names are used in place of a corresponding number ofdigits, and are printed in the directory in capital letters. For example, CARlton 2345, or NORth 6789. The letters of the alphabet are, of course, marked on the subscribers dial as well as the ten digits, as shown in Fig. 12.

The trunking between offices is along well-known lines, except that as before stated it is entirely independent of the numbering scheme. In general, each office is provided with first, second, and third selectors for selecting groups of inter-o'flice or local trunks, and with fourth and fifth selectors and connectors for completing local connections. Then, following the general plan, each otlice code will consist of three digits or series of impulses, which are produced by a suitable translation from the first three letters of the exchange name, and which serve to actuate the first, second and third selectors at the originating office to select an idle trunk in the group extending to the desired distant office, or a local trunk if the called party is in the same office. In either case, the trunk selected terminates in a fourth selector in the desired 'ofiice, which together with a fifth selector and connector serves to I complete the, connection.

It will be understood, therefore, that the general plan is to have direct trunks from. each ofiice to every other office and that these trunks are taken from the banks of the third selectors. This plan, however, needynot be rigidly adhered to and, in fact, is departed from in a good many cases. For instance, if all the inter-otfice trunks were taken from the banks of third selectors, one-thousand groups of trunks could be had, which is much more than is required in any known case. It is estimated that-not much over two-hundred ofiices will be re uired for the very largest systems, such as New York or London. In view of this, a large number of trunk groups can be taken from the banks of thesecond selectors to a considerable ad vantage. In a typical oflice, for example, eight levels in each of the nine groups of second selectors (the 0 level is used for Long groups of two-digit code trunks would make two-hundred-fifty-two groups in all.

Another departure from-the general plan introduces the featureof tandem trunking, which is desirable in many cases to secure efi'icient trunk groups. To illustrate, a number of offices in a distant area may have four-digit codes assigned, the first three digits of which are the same. In trunking calls to any of these ofiices the first three digits of the code would select a main group of trunks to the tandem office, a centrally located ofl'ice with respect to the others in the area'- in question, after which an incoming fourth selector in the tandem oiiice would respond to the fourth digit of the code to select a group of trunks to the particular o'ilicc desired. This arrangement would, of course, involve the use of fifth and sixth selectors in the offices reached by way of the tandem oflice, and usually in the tandem ofiice itself, although of course in many cases the main group of trunks to the tandem oflicc could be selected by a twodigit code instead of by athree-digit code in orden to avoid the use of sixth selectors.

The foregoing will give a general idea of the type of system to which the invention is applied, sufiicient to understand its operation and special uses. The drawings, of course, do not show a complete trunking systern, nor is this necessary in view of the extended knowledge of the subject. It has been-considered sufiicient to show a typical switch train, such as may be used to establish a connection between a calling station A, Fig. 1, in the originating oflice and a called station A, Fig. 5, in a tandem oiiice, and portions of several other switch trains, which show the routing .of calls from station A toother points; all of which will afford ample opportunity to explain the operation of the director.

Initiation of call.

The operation of the system will now be described in detail, it being assumed for this urpose' that the subscriber at'station A, ig. 1, desires to establish connection with the subscriber at station A, Fig. 5. \Vhcn the receiver is removed at station A, a circuit is completed over the line conductors 12 and 13 for theline'relay 18 of line switch C. Upon energizing, relay l8 closes a circuit for the switching relay 19 in series with the stepping magnet 20 at armature 26, and at armature 25 connects the test wiper 32 to this circuit at a point midway between the switching relay and the magnet. The operation now depends upon whether the test contact 36 with which the test wiper is inengagement is grounded or not grounded. If the trunk line shown is busy, the test contact 36 will be grounded, the switching relay 19 will be shtirtwircuited, and the stepping magnet 20 will be operated inter mittently, due to the fact that it interrupts its own circuit, to advance the switch wipers step by step in search of an idle trunk line. This operation is well understood, and it may be assumed, therefore, that at the time the subscriber removes his receiver and en- I is completed. Onattracting its armature 23, the switching relay disconnects the test wiper 32 from armature of the line relay 5 and connects it instead to its own lower terminal, the ground potential which is thus placed upon the test contact 36 being efi'ective to render the trunk line busy to other calls. In addition to the fore oing, relay 19 prepares a circuit for the meter Z at armature 22, and at armatures- 21 and 24 disconnects the line conductors 12 and 13 from the line relay 18 and, from ground, respectively, and extends them by way of wipers and 33, bank contacts 34 and 37, conductors and 42, and armatures 62 and 65 of relay 53 to the upper and lower winding of the line relay 5.0 in the relay group D.

lVhen the calling line is extended to the line relay'50 as previously explained, this relay is energized and at armature 55 closes a circuit for the slow-acting release relay 51. Upon energizing, 'relay 51 connects ground to the release trunk conductor 41 at armature 56, thereby closing a holding circuit for the line switch 0, which extends by way of the said conductor 41, test contact 36, test wiper 32, armature 23 and its working contacts, winding of the switching relay 19, and the winding of the stepping.

I magnet 20 to battery. This holding circuit is established before"v the slow-acting line relay 18 has had time to deenergize, and is effective to retain the line switch C in opers ated position throughout the connection. It will be observed thata ground potential is also placed on the private normal conductor 14 in order to render the calling line busy eflect of both of its windings, and since the windings are now in opposition the relay remains inoperative.

Oomwcting idle director to'trmtk.

Returning now to the relay group D, when relay 51 is energized, as before described, it removes ground from the test contact 101 at armature 59, and at armature 57 closes a circuit for the starting relay 86 "of the finder switch F as follows: From the grounded conductor 41 by way of armature 57 and its working contact, armature 61 and its resting contact, common starting wire 78, armature 112 and its resting contact, and the winding of starting relay 86 to battery. In the foregoing it is assumed, of course, that the finder F is idle at this time. When the circuit of the starting relay 86 is completed, the said relay is energized and at armature 114 completes a circuit for the switching relay 85 in series with the stepping magnet 89, while at armature 113 the test wiper 91 is connected to the above circuit at a point between the winding of the switching relay and the interrupter contact of the stepping magnet. If the finder is not already in engagement with the set of bank contacts as sociated with the trunk in use, it will now commence to rotate, but on the assumption that the wipers are in the position shown in the drawing, the test wiper 91 will find no ground potential on test contact 101, the normal ground connection to this particular test contact having been removed by the energization of relay 51, and no rotation of the switch will take place. The switching relay 85, however, is immediately energized and at armature 108 completes, a locking circuit for itself which extends from ground by way of armature 60; of relay 51, holding conductor 77, bank contact 102, wiper 92, armature 108 and its working contact, the winding of switching relay 85, and thewinding of stepping magnet 89 to battery. At

the same time that the foregoing circuit is 101, and also energizes relay 52, whichtakes ground-off the start wire 78 at armature 61. As a further result of the energization of relay 85, the starting-wire is disconnected from the starting relay 86 of the finder,

switch F, and when the startin relay deenergizes is transferred by way 0 conductor 78 to the starting relay of the next finder switch. v

As a further result of the energizationofswitchin rela 85, a bridge is closed across the trun con uctors 82 and 83 extending to the selector E Fig. 2, which may be traced from the upper trunk conductor 82 byway of contacts of relays 54 and 53, conductor 80, bank contact 104, wiper 94, armature 110 and its working contact, conductor 137, winding of polar relay 375, Fig. 8, resting cont act of armature 374 and the said armature, conductor 136, resting contact of armature and the said armature, working contact of armature122 and said armature, wiper 93,

bank contact 103, conductor 7 9, and the contactsof relays 53 and 54 to conductor 83. By the closure ofthe foregoing bridge, or loop, the line relay 400 of the first selector E is energized and completes a circuit for the slow-acting release rela 401. Upon energizing, relay 401 groun s the release trunk conductor 41 at armature 410, and at armature 408 prepares a circuit for the vertical magnet 407. The polar relay 375 is energized in series with. the line relay 400 of the selector E and the direction of current flow is such that theiarmature of the polar relay is operated to close a circuit for relay 378. Upon energizing, relay 378 completes av locking circuit for itself which extends from ground at the relay group D by way of armature 60, conductor 77, bank contact 102, wiper 92, armature 109 and its working contact, armature 119 and its resting contact, conductor 135, armature 384 and its resting contact, armature 388 and its working contact, and the winding of relay 37 8 to battery. Relay 378 also removes the short-circuit'from resistance 1- at armature 387, and at armature 390 prepares a locking circuit for relays 376 and 360.

A branch of the grounded conductor 135 may be traced from junction point 125 by way of the holding conductor 133 to Fig. 6, where the release relay 142 of the master digit controller M is now energized. Relay 142 removes ground from the'releasing conslow-acting relay 140, wiper 157 of the mas Setting the A impulse register.

Being advised by the signal thus transmitted to him that the exchange equipment isready for operation, the calling subscriber Wlll now proceed to operate the dial of his calling device in accordance with the three -deenergized four times.

significant letters and the four digits in the number of the called station. lVe will assume that this number is CARlton 2345. When the dial is operated in accordance with the letter C, four interruptions are produced in the calling subscribers line circuit inthe well-known manner, and the line relay of the relay group D- is accordingly At each deenergization relay'50 transmits an impulse of ourductor 160 at armature 148, at armature 159 1 separate conductors 398 and 399, and at armature 147 connects up the stepping magnet 163 of the time limit switch M This step. ping magnet is now intermittently operated under the control of the timer cam T which makes about one revolution every five seconds or more. The operation of this time limit switch will be neglected for the time being, and its function will be explained fully subsequent to the explanation of the regular circuit connection. It will be noticed also that the slow-acting relay 88 of the finder switch F is energized from the grounded holding conductor 77, and that this relay causes the energization ofrelay 124. The operation of these relays, however, is of no efiect at the present time.

1 Still another result of the energization of the switching relay 85 of the finder switch F is the preparation of an impulsing circuit for operating the registers; of the director.

This circuit may be traced from ground by way of armature of relay 50 and its resting contact (the circuit is now open at this point due to the energization of relay 50), working contact of armature 58.and the said armature, conductor 75, "bank contact 100, wiper 90, armature 106 and its working contact, armature 117 andits resting contact, conductor 134, winding of low resistance rent over the previously traced impulsing' circuit through the stepping magnet 155 of the A impulse switch M and the stepping magnet is operated to advance the wipers 170 and 171 into engagement with the fourth contacts in their respective banks. The low resistance relay 140 is energized i ri series with the stepping magnet 155, and being slow-acting retains its armatures attracted while the entire series of four impulses is being received. At armature 144 relay 140 .Qloses a circuit for the slow-acting'relay 141, and at armature 145 it closes a circuit for the release magnet 164 of the time limit control switch M This latter function is mentioned in passing in order that it may be understood that in the ordinary operatlon of the system this switch is released be fore it can perform any of its functions. Atthe end of the series of impulses the slow-actmg relay 140 deenergizes and breaks the circuit of slow-acting relay 141. During the interval between the deenergization of relay 140 and the deenergization of relay 141 an impulseof current is transmitted from ground by way of armature 144 and its resting contact, armature 146 and its working contact, and the winding of the stepping magnet 153 ofthe master dlgit control switch M to battery. Stepping magnet 153 is accordingly actuated to advance the wiper 157 to its second position. v A branch of the circuit of magnet 153 may be traced through the windmg of relay 143 to battery, which relay,

upon energizing, establishes a locking circuit for itself at armature,150.; At armaand conductor 175 to relay 200 of switch H Relay 200 is accordingly energized and at armature 204 opens the circuit of the release magnet 210. I

Setting the B a/mlU impulse registers.

When the calling subscriber dials the next letterof the number, or the letter A, two interruptions are produced in the line circuit, and the line relay 50 deenergizes twice, thus transmitting two impulses of current over the previously tr aced impulsing circuit to the vertical magnet 214 of the switch H. The impulses come in over conductor 176 and follow apath which extends by way of 011 normal springs 211 and 213, Winding of the slow-acting series relay 20.1, and the winding of the vertical magnet 214 to battery. By the operation of the vertical magnet wipers 220 to 223, inclusive, are raised two steps to a position adjacent the second level of bank contacts. Series relay 201 is energized at the same time as the vertical magnet 214, and maintains its armature 205 attracted in order to preserve the continuity of the impulsing circuit notwithstanding the shifting of'the off-normal springs which occurs on the first vertical step. At the end of the verticalmovement of the switch relay 201 retracts its armature and transfers the impulsing circuit to the rotary magnet 215.

During the transmission of the second series of impulses the slow-acting series relay 140, Fig. 6, is energized the same as it was during the transmission of the first series, and by cooperation with relay 141 transmits another impulse. of current to the stepping magnet 153 of the master digit control switch M. WViper 157 is thus advanced to its third position.

The calling subscriber may now dial the third letter whereupon the line relay 50 is again caused to d'eenergize twice, and transmit another series of two impulses over the impulsing circuitto the switch H Now, however, these impulses traverse the winding of the rotary magnet 215, and the switch wipers 220 to 223, inclusive, are rotated until they come to rest in engagementwith the second set of contacts in the second level. The slow-acting series relay 202 is energized during the rotary movement of the switch and closes a circuit for relay-203, which upon energizing, establishes a looking circuit for itself at armature 207.

Immediately following the transmission of the third series of impulses the stepping magnet 153 of the master digit control switch M is operated the same as before to advance the wiper 157 to its fourth position. In passing from its third to fourth position, wiper 157 transfers the impulsing circuit tothe stepping ma net 184 of the thousandths register switch h Se ndiwg the first 077706 Code dig i The calling subscriber will now,-of course, operate his dial in accordance with the four digits in the number, but before taking up the operation of the digit register switches, it will. be advisable to consider the operation of the sending switch S Fig. 8, which be gins to operate as soon as the switch H has completed its operation, to send out series of impulses in accordance with the oflice code which has been selected by the dialling of the first three letters in the called subscribers number. \Vhen the relay 203 in the switch H is energized at the beginning of the rotary movement of the switch, it closes a circuit over conductor 231 for the relay 379, .Fig. 8. Upon energizing, relay 379 short-circuits the polar relay 375 at armatime; 386. At the end of the rotary movement of switch H when the slow-actingrelay 202 falls back, it places ground on conductor 230 by way of armatures 206 and 208. Conductor 230 extends to the sequence switch S Fig; 9, where it is con'nected to the home or normal position contact of Wiper 318, and to the first,'second, third and fourth position contacts of wiper 317."It

follows, therefore, that when conductor 230- is grounded a circuit will be completed through wiper 318 and through the stepping magnet 321 of the sequence switch S to battery, and magnet 321 is accordingly operated to advance all the wipers. of the sequence switch to first position. The operation will be understood fully if it is re-' called that a switch of this type advances the wipers. when its armature is retracted. Thus on energizing, magnet 321 attracts its armature to engage another ratchet tooth, and at the same time breaks its own circuit. On deenergizing, the retraction of the armature under the tension of its spring drives the wipersinto first osition. and the initial energizing circuit 0 magnet 321 is broken by wiper 318. 1

The code of the distant ofiice in which the line of station A terminates is 34, as will be perceived from an inspection of Figs. 2 and 3, which show that the trunk line comprising conductors 541 and. 542 is accessible from the fourth level of the thirdgrou of second selectors in the originating. 0 cc.

'Aceordingly, the second set of contacts in tively. These cross connections will cause the required series of impulses to be. transmitted by the sending switch S, as will be understood shortly.

When the sequence switch wiper 319 arrives in first position, it places ground on the No. 3 bank' contact associated with the stop wiper 364 of the sending switch S, the circuit Being traceable as follows: Grounded wiper 319 in first position, con duct-or 224, wiper 226 of switch H and bank contact engaged thereby, terminal 257 on i the I.D.F., a jumper, bus-bar 3,\ and conductor 243 to the No. 3 contact in the lower bank of switch S The grounding of this contact determines that there wilhbe three IIItGl'I'UPlZlOIlS in the first series transmitted. Wiper 317, on arriving in first position,

closesa circuit for the impulsing relay 362' of the sending switch S as follows "From the grounded conductor 230, by way of wiper 317 in first position, conductor 340, resting contact of armature 368 and the said armature, windingof relay 362 and the machine interrupter I to battery. The interrupter I is continuously driven, and consistsof any suitable cam arrangement for intermittently connecting battery to the relays such as relay 362, at the rate of about ten times per second. When its circuit is closed, therefore, or shortly afterwards, depending, on the position of the interrupter I, relay 362 is energized and opens the impulsin'g contact 374, this operation being of no effect, however, due to the -fact that the contact at armature 374 is short-circuited at armature 371 of relay 361. Relay 362 also closes a circuit for stepping magnet 365 at armature 373, and the said magnet is energized' When the circuit of relay 362 is broken by the interrupter I an instant later the said relay falls baclaagain closes its'interrupter Contact, and breaks the circuit of the steping magnet365, which thereupon retracts its armature and advances the wipers 363 and 364 one step. A circuit is now completed for relay 361 by means of wiper 363, and this relay, upon energizing, removes the short-circuit from around the impulsing contact 374 at armature 371,.and at armature 372 closes a'circuit over conductor'341 for the stepping magnet 32].- of the sequence switch S Magnet 321 is accordingly energized, but without alieeting the pos tion of its wipers, which as previously explained, are advanced upon the denergization of the stepping magnet. The second time that the circuit of relay 362 is closed by the interrupter I, the said relay closes the circuit of the stepping magnet 365 as before, and also,

since relay 361 is now energized, at armature 374 it breaks the circuit of the line relay 400 of the selector E hen the circuit of relay 362 is broken by the interrupter, it

deenergizes and breaks the circuit of the 1 stepping magnet 365, which retract-s its armature and advances wipers 363 and 364 one more step, thus bringing the stop wiper 364 into engagement with the number 1 contact in its bank. It will be seen that the sending switch S is caused to make an initial or false step before it actually begins transmitting impulses, and this, it may be stated,.is' done in order to insure that the first impulse transmitted will be of the standard length. The energizations and deenergizations of the relay 362 continue in quick succession under the control of the interrupter 1. After the second deenergization, which terminates the first interruption.

wiper 364 is advanred into engagement with its No. '1 contact, as stated, after the third dcenergization wiper 364 isadvanced into engagement with'its No. 2 contact. and'after thefourth .deenergization the said wiper is advanced into engagement with its No. 3

contact. The required number of interruptions have now been produced in the circuit of the line relay 400 of the selector E As .previously.explained, the No. 3 contact in the lower bank of sending switch S is grounded, and when the stop wiper 364 comesinto engagement with this contact a circuit is completed for the stop relay 360 and relay 37 6 in parallel. Upon energizing, relay 376 closes a locking circuit for itself and relay 360 which extends from ground by way of armature 39011141 its working contact, resting contact of armature 385 and said armature, resting contact of armature 394 and said armature, armature 382 and its working contact, and the windings of relays 376 and 360 in parallel to battery. Relay 376 also removes the short-circuit from the polar relay 375 at. armature 381.

Relay 360, on energizing, opens the circuit of the impulsing relay 362 at armature 368, to stop the transmission of impulses, and in addition, at armature 366, closes an automatic stepping circuit formagnet 365, which now operates automatically under the control of wiper 363 to advance the sending switch to normal position. When the sending switch wipers reach their normal position, wiper 363 will no longer'find ground and the magnet 365 will cease its operation.

Also relay 361 is deenergized, at armature iii-0 armature 372. {Magnet 321 is'accordingly deenergized to advance the wipers of the sequence switch to second position. The only change brought about by. the advance ductor 225, wiper 221, terminal 256, a

jumper, No. 4 bus-bar, and conductor 244 to the No. 4 bank contact associated with the stop wiper 364.

Although the sending switch S has been returned to normal, the stop relay 360 and the relay 376 still remain locked up, due to the previously described locking circuit. The latter relay, it should be noted, removes the short-circuit from, the polar .relay 375 at armature381. 1

Operating the first selector.

The operation of the selector E responsive to the first series of impulsesof the code may now be considered. As explained before, the circuit of the line relay 400 is interrupted three times at Contact 374 of the impulsing relay 3G2, and the said line relay accordingly deenergizes three times and at armature 418 transmits three impulses to the vertical magnet 407. In response to these impulses the vertical magnet operates to raise the selector shaft step by step until the wipers 420, 421, and 422 reach a position opposite the third level of bank contacts. Slow-acting series relay 402 is energized in serieswith the vertical magnet 407, maintains its armature 409 attracted throughout the vertical movement of the switch, and as soon asoif normal springs 413 close on' the first vertical step, completes a circuit for the stepping relay 403. Upon energizing,

relay 403 closes a locking circuit for itself at armature 411 and at armature 412 prepares a circuit for the rotary magnet 405. At the end of the vertical movement of the switch relay 402 falls back and at the resting contact of its armature 409 completes the rotary magnet circuit. T he rotary mag-.

net 405 is, therefore, energized and advances the wipers into engagement with the first set of contacts in the level opposite which they were raised. 'Atthe same time the rotary magnet breaks the locking circuit of the stcppingrelay 403, and the stepping relay deenergizes and breaks the circuit of the rotary magnet atarmature 412, whereupon the rotary magnet deenergizes also and again closes its interrupter contact. The Operation now depends on whether the test-contact engaged by the test wiper 421 is grounded or not. If the first trunk line terminating in the third level is busy, the

test contact associated with such trunkline will have a ground potential on it, the

switching relay 404 will be short-circuited,

ing conductors 440, 441 and 442, and extend ing to the second selector E lVhen the test wiper 421 is brought to rest in engagement with test contact 424, it finds no ground potential and it follows, therefore, that on the retraction of the armature of the rotary magnet 405, the stepping relay 403 will not be energized. Instead. the switching relay 404, which for the time being has been short-circuited, is energized in series. with relay 408, the high resistance of relay 404 preventing the latter relay from operating. On energizing, relay 404 connects the release trunk conductor 41 to the test wiper 421, thereby grounding test contact 424 and making the selected trunk line busy. In addition, relay 404 removes ground from the line relay armature at its armature 414, and at armatures 415 and 417 relay 404 disconnects the incoming trunk conductors 82 and 83 from the windings of the line relay 400 and extends them by wav of wipers 420 and 422, bank contacts 423 and 425, trunk conductors 440 and 442, and

armatures 456 and 455 to the windings of the line rela 450 of the second selector E Line relay 450 is accordingly energized and closes a circuit forthe slow-acting release .relay 45L At its lower armature relay 451 prepares the switch for its vertical operation in the, usual manner, and at its upper armature connects ground to the release trunk conductor 441, thus establishing a holding circuit which extends by way of conductor 441, test contact 424,tcst wiper 421, and armature 416 and its working contacts to the release trunk conductor 41. The holding circuit including conductors 441 and 41, except that it is grounded furthcr along in the connection, will be used later on to retain the switches involved in the connection in operated position.

Send Jag the second oflice code dig it.

will be reversed also, resulting in the operation of the polar relay 375. Relay 375 now operates its armature in the properdirection to close the circuit of relay 377, which -repares a locking circuit for itself at armature 383, and breaks the locking circuit of relay 378 at armature 384. The latter relay accordingly falls back, whereupon the previously prepared locking circuit for relay 383 is completed at armature 389. When relay 377 energizes, at its armature-385 it removes ground from armature 382 of relay 376, and since ground is not reapplied to armature 382 until relay 378 has had time to fall back, the locking circuit for relays 376 and 360 is broken longenough to permit the former relay to retract its armature 382, which permanently opens the locking circuit and permits both relays to remain deenergized.

The foregoing is descriptive of the operation provided the sending switch S reaches its normal position before the polar relay 375 is operated. It may happen, however, as for example when a short series of. impulses is transmitted, or when no extended trunk selecting operation of the selector is required, that the polar relay is operated first, in

which case the relays 360 and 376 will not be unlocked by the operation of the olar relay and relay 377, but will be hel u until the sending switch returns to norma This is taken care of by relay 395. Assuming that the sending switch S is still rotat-- ing whenthe polar relay and relay 377 are operated, the relay 361 will be in energized position, and when relay 377 opens the looking circuit of relays 360 and 376 at armature 385, these relays will be held up over a new circuit extending from ground by way of armature 370 of relay 361, armature 393 and its resting contact, winding of relay 395, armature 382 and its working contact, and the windings of relays 360 and 376 in parallel to battery. Relay 395 is at once energized and at armature 394 opens the previous locking circuit. Then when the sending switch eventually arrives at its normal position, the deenergization of relay 361 opens the circuit of relays 395, 360, and 376 at armature 370, and all these relays deenergize,.the original locking circuit being broken. at armature 382 before it: can be reestablished at armature 394.

The second series of code impulses is .now transmitted similar tothe manner in which the first series was transmitted. When the stop relay 360 falls back it completes the circuit for the impulsing relay at armature 368, and this relay is accordingly operated intermittently by the interrupter I to pi advance the wipers of the sending switch step I by step through the medium of the stepping magnet 365. At the first step of the switch,

relay 361 is energized, closes the circuit of the stepping magnet 321 of the sequence 362 to interrupt the circuit of the line relay 450 of the second selector E each time it closes the circuit of the stepping magnet 365. Thus four interruptions will be produced in the circuit of said line relay by the time the stop wiper 364 arrives at the No. 4 contact in its bank. The No. 4 contact is now grounded, as previously. ex lained, and relays 360 and 376 are accor ingly again energized, a locking circuit being established at armature 382 as before. Relay 360 also breaks thecircuit of the impulsing relay 362 at its armature 368, and at ,armature 366 closes the automatic rotary circuit for the stepping magnet 365, by means of which the sending switch is advanced to normal. Relay 361 then falls back and at armature 372 breaks the circuit of the magnet 321 of sequence switch S whereupon the sequence switch wipers are advanced to third position.

Skipping the third and fourth oflice code digits.

The operation of the second selector E responsive to the second series of code impulses and the subsequent operations which resultin the extension of the connection to the repeater R, Fig. 3 will be deferred awhile to permit the explanation of operations in the director which result from the advance of the sequence switch to third position. It may be explained that the provision of four wi ers, on the Strowger switches, such as t eswitch H and the circuit arrangement by which these Wipers are grounded successively by the wiper 319 of tie sequence switch renders. it possible to transmit codes comprising a maximum of four series of impulses, which is thought to be sufiicient in most cases, although additional series of impulses can be provided for by adding more wi ers and banks to the Strowger switches. 11 the present case, since the code consistsof onl two series of impulses, the sequence switc must be advanced automatically through its third and fourth positions, in order to have the director ready for the transmission of the impulses corres onding to the thousands digit as soon as t e second selector E" and the secondary line switch 0 have completed their operations. This is accomplished by connecting terminals 255 and 254 to the special. bus-bars 271 and 270, respectively, .instead of to any of the upper bus-bars arrives in third position, a

in third position, conductor 226, wiper 222, terminal 255, a jumper connecting said terminal with bus-bar 271, conductor 238, wiper 318 in third position, the interrupter contact of magnet 321, and through the wind- .ing of said magnet to battery. The completion of this circuit causes a momentary energization of magnet 321 to advance thesequence switch wipers to fourth osition, whereupon a similar circuit is comp eted b way of the grounded wiperv 319 in fourth position, conductor 227, wiper 223, terminal 254, a jumper connecting said terminal with vance the sequence switch wipers into. the

fifth or thousandsposition. These operations of the stepping magnet 321 take place very rapidly, and the sequence switch is advanced. through its third and fourth positions in a small fractionof a second.

Operating the second selector and the outgoing secondary Zine switch.

The operation of the second selector E, Fig. 2, responsive to the second series of impu ses of the oifice code may now be considered. As before explained, four interruptions are produced in the circuit of the linerelay 450, and this relay is accordingly deenergized momentarily four times toraise the wipers 460, 461, and 462 opposite. the fourth level by means of the vertical magnet 457. In view ofthe explanation of the operation of the first selector E which has already been given, it will be unnecessary to explain in detail how the second selector E o crates; but it will be su'flicient to say that a ter the wipers are raised to the fourth level they are automatically rotated by the rotary magnet 458 until an idle trunk lineis' reached. Assuming that the first idle trunk line encountered is the one comprising conductors 500, 501 and 502 extending to the Secondary rotary line switch C Fi 3, when the selector wipers arrive at ban contacts 463, 464, and 465' the rotation of theswitch will cease and the switching relay 454 is energized.- At its armature 459 the switching relay 454 connects the release trunk. conductor 441 to the test wiper 461 in order to make the selected trunk line busy; and at its armatures 456 and 455 the switching relay 454 disconnects the trunk conductors 440 and 442 from the windings of the line relay 450, and extends them by way of wipers 460 and 462, hank contacts 463 and 465, trunk-conductors 500 and 502, and armatures508 and 511 of relay .503 of the line switch \ilfto the winding of the line relay 504 and' -';to ground,*=-'respectivelv.

When. the connection is extended tdtli'e line switch Chas previously described, the line relay 504 is energized and at armature 507 connects ground to the release trunk icon ductor 501. taina local aground on'the, test contact 464 after the slow-acting rela' 4510f the selector E has fallenback.

also closes a circuit for the'switchingrelay .503 in series with the stepping magnet 512 at armature 506, while at armature 505 1t connects the test wiper 521 to the circuit of his operationserves to 'main-.

he line relay 504 the switching relay at a pointbetween said relay and the interru ter contact of the step ping magnet. If 1 t e wipers of the line switch are standing ona busy trunk line, the switch now operates in the well-known manner to advance its wipers through' the ns-'1 dium of the stepping magnet 512 to an idle trunk line, but if the trunk line upon which the wIpers are standing is idle, as will be assumed to be the case, no rotation of the 4 switch will take place. Instead, the switch-f ing relay 503 is immediately energized, and

at its armatures .509 and 510 connects the inco'min release trunk conductor 501 with the I test w1per 521 in order to make theselected trunk line busy by grounding the test contact 524. At the same time, of course, the

test wiper is disconnected from the test cir.

cuit at the resting contact of. armature 510.

In addition to the foregoing, at armatures 508 and 511 the switching relay disconnects the incoming trunk conductors 500'and 502 y from the line relay 504 and from ground,

respectively, and extends them by way of" wipers 520e and 522, bank contacts 523 and f W on the connection is extended to the repeater R as explained in the foregoing, the

linerelay 535is energized and completes a circuit for the slow-acting release relay 536 at armature 538,, On energizing, relay 536 places ground on the release trunk 'conduc tor 527 at armature 540, and thus establishes a holding circuit wlnc includes release trunk conductors 527, 501, 441,- and 415. This holding circuit is still grounded atiarmature -56 of relay 51 in the relay group D, Fig. '1;

but the ground at this point, is. only. .tem-I "12f;

porary as will appear subsequently, and after the use of the director is dis ensed with the groundat the repeater R wi I serve to ,main-.

tain all of the various switches so far con-,

sidered in operated position. It'is noted at thistime that the righthand winding of the shunt field relay 533 is energized from the groundedrelease trunk conductor 527; at the repeater R. Owing to the fact, however,

that the right hand core of relay 533 has a complete magnetic circuit including the left 

